1. Field of the Invention
The present invention relates in general to the cooling process during shape melting, and, in particular, to an automatically controlled cooling device designed to cool the workpiece during the shape melting process at an optimum cooling rate and to maintain an optimum interpass temperature.
2. Description of the Related Art
As used herein, the term shape melting is used to refer to a welding process whereby structural components are manufactured entirely from weld material deposited layer-upon-layer onto a surface or an initial preform until the desired geometry is achieved. This process offers the advantage of delivering a near net shape component that can be produced quickly and economically using either ferrous or non-ferrous materials.
A significant amount of heat is generated during the shape melting process. The source of this heat is a welding arc which is used to melt and deposit material. The heat input for shape melting might range from 10 kilojoules per inch to as high as 400 kilojoules per inch (for some high deposition rate processes). Even at the low end of the heat input range, if no means of extracting heat is provided, the heat input of the shape melting process will cause the average temperature of the workpiece to continuously rise. It is necessary to maintain a maximum average workpiece temperature in order to control the properties of the final product. The average temperature also impacts the amount of distortion in the product, the bead shape, the degree of oxidation, and perhaps the weldability of the deposited material. For these reasons it is desirable to maintain some maximum average "interpass" temperature.
Similar considerations (mechanical properties, weldability, distortion, etc.) also dictate that maintaining a maximum interpass temperature and an optimum cooling rate is prudent. So, to successfully manufacture a shaped melted component, a high degree of temperature control is necessary.
Various investigators have developed methods and apparatus related to the shape melting process, with particular emphasis on the cooling process. U.S. Pat. No. 3,985,995 to Brandi, deceased et al discloses a cooling process using sprays of water or jets of air for pre- and post-cooling around the weld metal deposition to locally cool the work piece. Likewise, U.S. Pat. No. 3,948,428 teaches of a device using water and gas wherein the cooling water is brought into contact with a hot weld and wherein the generated steam and non-evaporated water are immediately removed from the weld. U.S. Pat. No. 4,517,434 teaches the use of cooling with carbon dioxide by admixing it in the solid state with the welding powder.
German Patent Disclosure No. 2,942,868 discloses a device for locally cooling a welding zone in front of and/or behind the particular weld point by means of liquid and/or gaseous media. The device consists of at least one unit with a nozzle directed towards the workpiece for spreading a cooling fluid, and placed in a directing funnel with a hood surrounding the directing funnel connected to a vacuum device. Vapors created by the cooling process are immediately aspirated. Several units can be used to increase the cooling performance, and have a means for operating in an excess of a 90.degree. angle. UK Patent Application No. GB 2,061,156A modifies this cooling approach with the addition of an exhaust duct to indirectly remove cooling vapor and radiant heat.
The time at which the coolant is removed is another approach taken in UK Patent Application No. GB 2,160,809A by removing the water-air mixture before the formation of steam.
Other approaches to cooling the workpiece involved techniques for rebuilding tractor-roller assemblies such as U.S. Pat. Nos. 4,230,928; 3,514,568; 3,596,041; 3,895,209; and 4,233,487.
Still other attempts at cooling the workpiece for shape melted components include: employment of a water cooled dam, U.S. Pat. No. 3,696,228; an outer jacket forming a coolant chamber, U.S. Pat.No. 2,912,562; U.S. Pat. Nos. 3,071,678 and 3,179,783; a water cooled welding torch, or some modification thereto such as U.S. Pat. No. 4,140,892; and cooling of the workpiece holder like in U.S. Pat. Nos. 3,777,106 and 3,953,704.
Many of the features of the prior art are also described in a literature article on shape welding, "High Quality Large Components `Shape Welded` By A SAW Process", Kussmaul, K., Schoch, F. W., and Luckow, H., Welding Journal, September, 1983.
Evaluation of the above-mentioned references reveal many attempts to address the need for a device to cool at a desired rate or to within a given temperature range, however, in every instance no indication is given as to how the device is precisely and accurately controlled to achieve the desired cooling response.
There is a need for a device which has the ability to sense the temperature of the workpiece, and to adjust the total coolant flow rate through the device for optimum cooling. The prior art shows the need for an apparatus that when the temperature of the workpiece varies upwards at different rates during manufacture, it will cool at different rates maintaining a constantly acceptable interpass temperature.